[Xen-users] Xen domU hangs after running xtrabackup with MariaDB

[Tomas Mozes <hydrapolic@xxxxxxxxx>]

Hello,
since upgrading to Linux kernel 4.4 we are observing strange server hangs on domU after database operations. This happened on two distinct servers (one is like 3 years old, another one is brand new):

A) server acting as a Mariadb slave and running Percona Xtrabackup
B) new server running a Mariadb restore from sql dump or after running Percona Xtrabackup

The xtrabackup process is in uninterruptable state and some files in /var/lib/mysql cannot be even read (cat hangs) - after xl destroy/create they are readable again.

The dom0/domU are running Linux kernel 4.4.24, Xen 4.6.3. The databases are on lvm volumes with xfs. We could at least complete a backup when we disabled O_DIRECT for Mariadb. We were succesfully running Linux kernel 4.1 with older Xen (4.6.1 IIRC) with lvm/xfs and O_DIRECT before without such hangs.

The bug reports with some more details at Mariadb/Percona:
https://jira.mariadb.org/browse/MDEV-10852
https://bugs.launchpad.net/percona-xtrabackup/+bug/1625984

What information could help tracing this problem down? At least the output of echo {l,m,w} > /proc/sysrq-triggers are attached to the bug reports.

Thanks,
Tomas Mozes

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